Long-duration energy storage (LDES) covers technologies that can store electricity and release it over many hours or even days. Ofgem’s support scheme defines long-duration electricity storage as at least eight hours of output at full power. Most grid batteries built so far discharge for two to four hours.
Why it matters
A grid that runs mainly on wind and solar needs to cover still, cloudy spells that can last for days, and to use surplus power that would otherwise be curtailed. Short-duration batteries help within a day; LDES shifts larger volumes of energy over longer periods and could reduce reliance on gas plants as backup. No new large-scale long-duration storage has been commissioned in Great Britain for decades, largely because the projects are expensive and their future revenues uncertain.
Technologies
| Technology | How it stores energy |
|---|---|
| Pumped storage hydro | Pumps water uphill to a reservoir, releases it through turbines |
| Compressed air | Stores air under pressure, often in underground caverns |
| Liquid air | Cools air until it liquefies, then expands it to drive a turbine |
| Flow batteries | Pumps liquid electrolytes, such as vanadium, through a cell |
| Long-duration lithium-ion | Standard battery cells sized for eight hours or more |
Ofgem’s cap and floor scheme
The government confirmed in 2024 that it would support LDES through a cap and floor scheme run by Ofgem. If a project’s revenues fall below a floor, consumers top them up through bills; revenues above a cap are shared back with consumers. The first application window ran from April to June 2025.
On 26 June 2026 Ofgem published its minded-to decision for window 1, provisionally selecting 16 projects with about 7.65 GW of power and 136.9 GWh of storage, with durations of 8 to 22 hours. They comprise 11 lithium-ion battery projects, 3 pumped storage hydro schemes, 1 compressed air project and 1 vanadium flow battery. The consultation closed in August 2026. As of early October 2026, Ofgem had not published final decisions, which it expects in autumn 2026.
Read more: Pumped storage hydropower: the UK’s biggest battery.